Photographic materials are generally prepared by coating at least one photographic photosensitive layer on a plastic film support. A fiber based polymer as typified by triacetylcellulose (referred to hereinafter as "TAC") or a polyester based polymer as typified by poly(ethylene terephthalate) (referred to hereinafter as "PET") is generally used for the plastic film.
In the past, PET films have replaced TAC because of their excellent production properties, mechanical strength and dimensional stability. Even though PET films have the excellent properties indicated above, their use results in a low film hardening rate after manufacture, and lower productivity, such that the range of application is limited. On the other hand, the greatest advantages of TAC films as supports for photographic purposes include the lack of optical anisotropy and high transparency.
TAC films also have a further advantage in that the film hardens rapidly after manufacture.
There has been considerable diversification of the types and applications of photographic materials in recent years, and remarkable progress has been made with increased film transporting rates during photographing, increased magnification in photographing, and with the miniaturization of cameras. At the same time, there have been increased demands for supports for photographic materials having the properties of strength, dimensional stability and reduced film thickness, etc.
However, the properties of TAC are dictated by a rigid molecular structure, and films made from TAC are brittle and weak, such that TAC films cannot at the present time be used in these applications.
On the other hand, although PET films have excellent mechanical strength, they are disadvantageous in that the film hardening rate after manufacture is slow to the point of being impractical, and it is therefore desirable to solve this problem.